Researchers have suggested that the risk of eruption of a "supervolcano", hundreds times more powerful than conventional volcanoes -have potential to wipe out civilization - is more likely than believed earlier.
By effectively "exploding" as opposed to erupting, supervolcanos leave a giant hole in the Earth's crust - a caldera, that can be up to one hundred kilometres in diameter.
A supervolcano's magma chamber can be several kilometres thick and up to one hundred kilometres wide, which makes it far too big to sustain sufficient overpressure through magma recharge.
For the magma to break through the crustal rock above the magma chamber and carve out a path to the surface, it needs an overpressure level that is 100 to 400 times higher than air pressure (10 to 40 megapascals).
A team of researchers headed by ETH-Zurich professor Carmen Sanchez-Valle has now identified a trigger for supereruptions by determining the density of supervolcanic magma, using an X-ray beam at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France.
The scientists used a special press to study artificially produced magma melts under the same extreme pressure and temperature conditions as inside a volcanic magma chamber.
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Both the melts and the pressure and temperature conditions corresponded to the natural conditions of a supervolcano.
Moreover, the researchers varied the water content of the melts. Via the different parameters, they formulated mathematical equations, which helped them to reconstruct the conditions in a supervolcano.
Supereruptions generally eject at least 450 but sometimes even several thousands of cubic kilometres of rock material and ash to the surface and into the atmosphere.
In the event of explosive eruptions, ash and rock fragments with their environmentally harmful chemical components can rise over thirty kilometres up into the atmosphere and have a devastating impact on the climate and life on Earth.
The study has been published in the journal Nature Geoscience.